Energy consumption of residential and commercial buildings is responsible for nearly 40% of the total energy use in the word. In a typical building, windows could be the major source of energy loss, or gain, depending on their design. For modern buildings, the design of energy saving and environmentally-friendly atmosphere is becoming more and more important. To this end, using solar-adjustable smart windows to replace current static windows could be an efficient way. Smart windows with tunable transmittance levels can block or reflect sunlight on scorching days to lower energy consumption by air conditioning appliances. Such windows can also be put in a transparent state to improve light harvesting in a low lighting condition, or to enhance heat capture in cold weather. Moreover, with such a technology, depending on personal preferences, transmission of solar radiation into buildings can be controlled, so as to tune visual contact between indoors and outdoors for privacy and comfort.
In recent years, various reversibly switchable smart windows have been investigated and developed. Among them, smart windows based on chromogenic materials, liquid crystals and suspended particles have been attracting increased attention. Basically, there are four kinds of materials that can be used for chromogenic windows: electrochromic, photochromic, thermochromic and gasochromic. However, these chromogenic devices have some drawbacks that are not suitable for commercially large-scale fabrication and building applications. For example, electrochromic windows [U.S. Pat. No. 8,164,818B2] that can achieve tunability by oxidation/reduction reactions of chromogenic materials driven by the insertion/extraction of ions and electrons are not structurally stable because chemical reactions are involved. Thermochromic windows [U.S. Pat. No. 9,442,313B2] suffer from high transition temperature, low visible transmittance, unattractive visible colors and limited modulation. Liquid crystal devices [U.S. Pat. No. 3,731,986A] are usually limited to fabrication on rigid glass substrates and require continuous power supply, which entails a high power consumption. Their long-term ultraviolet (UV) instability and high cost remain critical issues as well.
Suspended particle-based smart devices, also called dipole particle suspension devices [US20130033741A1] usually use elongated, rod-like particles as an active light-controlling component. Their operation is based on the variation of orientation of elongated particles upon the application of an external electric field, which changes the optical absorption, reflection and scattering of composites, and thereby the transmission of the photon flux. The suspended particle device (SPD) has two distinctly different states: on and off. When an external electric field is applied, the particles are polarized and rotate under the torque exerted by the electric field and align themselves with applied field. As a result of increased particle alignment, more photons can pass through the medium and light transmittance increases. When the electric field is switched off, particles relax and become randomly oriented in the medium, thereby blocking more photons. Because the operation of these SPDs is based on the polarization and rotation of particles, which is essentially a physical process, such devices are free form the issues associated with electrochromic windows, as mentioned above. Different from most of the liquid-crystal devices, SPDs can integrate well on flexible substrates with low power consumption, therefore they have another advantage for next generation of flexible, low-cost smart windows.
Quantum dots (QDs), also referred to as semiconductor nanocrystals, are normally composed of II-VI, IV-VI or III-V compounds. They have attracted considerable attention in the past two decades due to their potential applications in light-emitting diodes, solar cells, and diodes lasers owing to not only their unique optical features, such as broad excitation spectra, narrow emission bands, high molar extinction coefficient, size-dependent optical absorption and emission spectra, but also their room temperature solution processibility, facile fabrication of multijunction solar cells and potentially efficient multiple exciton generation and hot electron extraction. Typically, the QDs are smaller than 100 nm in dimension and show novel properties different from their bulk counterparts. Near-infrared (NIR) emitting QDs, which can be tuned to emit from below 1000 to several thousand nanometers, are particularly interesting. Compared with visible (vis) QDs (e.g., CdS and CdSe), NIR QDs, such as PbS, Ag2S, PbSe, absorb photons not only in the UV and vis ranges, but also in the NIR range. They have been directly used and have also been coupled with various other materials for diverse applications. For example, D. Ma' group [Adv. Funct. Mater. 2011, 21, 4010] successfully coupled PbS QDs with multi-walled carbon nanotubes and then integrated this nanohybrid with a hole transporting polymer of poly(3-hexylthiophene) (P3HT) to fabricate bulk heterojunction solar cells, which considerably extend the photon-to-charge carrier conversion into the NIR range and exhibit a largely enhanced power conversion efficiency of ˜18% as compared to the control P3HT: [6,6]-Phenyl-C 61-Butyric Acid Methyl Ester (PCBM) solar cell fabricated under the same conditions.
Considering the unique properties of the QDs, in particular, their broad absorption and large absorption coefficients, their combination with suspended particles (for example organometallic nanorods) is expected to lead to the improvement of tunability of optical properties over a wide wavelength range.
The objective of the present invention is to provide quantum dots integrated organometallic nanorods and the method to make such a nanohybrid.
It is now also the objective of the present invention to provide a method to assemble a light transmission controlling device using the nanohybrids in this invention.